In the late 1800s and early 1900s, Europeans explored Chinese Turkestan and there salvaged / excavated / bought manuscripts and fragments thereof in Old Uighur and in languages used by ethnic-groups that the Uighurs had assimilated, such as Northwestern Prakrit, which had been employed along the Southern Route of the Silk Road by a basically-Tocharian population (to judge from names in the texts), who wrote it in Kharoṣṭhī script. Along with this book of translations, you may likely want to use the same author's _Language of the Kharoṣṭhī Documents from Chinese Turkestan_ and images of the documents, some of them available for instance on the web-pages of IDP in London and more being given along with the first edition of these texts by Rapson et al. and/or in vol. IV of Aurel Stein's _Serindia_. Also, if you use the search-term "Kharoṣṭhī", you can turn up studies concerning the script itself as well as other texts in this language (along with editions of them), such as the _Khotan Dharmapada_, and ones that have come to light more recently.